There are many situations in which it is desirable to prevent small animals such as squirrels from passing along a suspended cable. For example, it is desirable to keep rats from climbing along ships hawsers, squirrels from climbing along cables to reach a bird feeder, or squirrels or other small animals from climbing along power lines, especially the overhead getaways running into electrical substations.
The most commonly used protector is a large disc mounted to the cable, such as that shown in U.S. Pat. Nos. 2,493,107, and 4,523,546. These discs suffer from a number of drawbacks which prevent them from being successful animal barriers on horizontal cables. For one, since squirrels can jump many feet, the discs would need to be very large to prevent squirrels from simply jumping over the device. Frequently, electrical cables including overhead getaways are spaced relatively closely together, and there is insufficient room for such large discs. Further, the large discs create a severe wind loading problem which may not be acceptable.
Another type of aerial cable guard is disclosed in U.S. Pat. No. 4,262,169. The patented device is designed to prevent animals from chewing on the cable; the device is counterbalanced to maintain it in an upright position. When an animal steps on the top, the device rotates to prevent the animal from getting at the cable. However, squirrels are very adept at walking "hand over hand" upside down along the length of an object, and thus could simply use the patented device as a walkway. In addition, since squirrels can jump many feet, the device would have to be extremely long to prevent the squirrels from simply jumping over it. Further, since the guard is not symmetrical on the wire, a cross wind could cause it to spin.
Another device, U.S. Pat. No. 4,867,104, is designed to prevent squirrels from climbing up from below and reaching the bird feeder. The device has a number of small rotating blocks mounted on a fixed shaft. However, if used in a horizontal orientation, since the blocks are all of the same size, a squirrel would be able to balance on the blocks sufficiently to allow it to run across their tops, or even climb along their bottoms, to defeat the device. In addition, on a horizontal cable there would have to be many feet of such blocks to prevent the squirrel from simply jumping over the guard.